Like $1.24 with free shipping. I bought 2, from 2 “different” sellers. Will gut them and take pix when they arrive.
I’ve bought small quantities (~10) of those servo testers direct from china for under 15 cents a piece. Can’t imagine what they must sell for in bulk. Unfortunately a bunch got stuck at the Chinese border because they thought they were lithium batteries :(.
That particular model is kind of interesting, it also uses a PIC knockoff but it’s a through hole (~16 pin) DIP package instead of a surface mount one. I think they might of had trouble fitting the additional button needed for things like sweep mode on a single layer PCB with the SMD chip so they switched to a through hole chip to pack things more efficiently. (EK2-0907 is a 2 layer pcb which costs more)
Looks like it was soldered by hand too… Makes me wonder about the work conditions there.
My two cents…
While I won’t say the working conditions are good it is important to remember that before China became a manufacturing powerhouse the majority of the workforce were farmers. There were no middle class desk jobs accessible for the average person. As these hard labour farming jobs dried up China smartly transitioned to a manufacturing economy and while the pay may not be great these factories often provide onsite food, housing and childcare which covers the majority of expenses. Many of the workers would have trouble finding any work at all if these factory jobs were unavailable and the outcome would be pretty grim.
There was a big media uproar a couple of years ago when the manufacturer well known for producing Apple products, Foxconn installed suicide nets around their worker’s dormitories. From our western viewpoint this can seem pretty appalling but in reality the suicide rate among Foxconn factory workers were lower than China as a whole. We like to ignore that we might also share some of the same problems.
We’ve been using these same ones for about 3 years now. Its mounted on a board with two motor controllers and an Anderson sb50 connector.
Power for the servo tester comes from an lm7805 that taps off the 12v leads that go to the controllers.
Just plug in a battery + motors and go.
This board comes up in the mode where output speed is controlled by the pot, pressing a button under the plastic shroud changes between modes. These other modes can be dangerous depending on what mechanism you’re hooking u p to. It might be worth removing the button from the board for safety reasons.
One came in the mail Monday. Hooked it up (powered by 3 AA cells soldered in series)… works fine. Keep reading for simple way to get rid of the need for the batteries.
Every FRC team can have a motor tester for very little cost.
Power for the servo tester comes from an lm7805 that taps off the 12v leads that go to the controllers.
Yes. You can buy DC-DC step-down converters on eBay for 74 cents (with free shipping). Just connect the input to a tap off the FRC battery 12V, and the 5V output powers the servo tester (PWM signal generator).
I bought 8 different models (using various chips, both switching and linear) for evaluation. Will post again when they are received and tested.
Here’s a pic of one of the DC-DC converters (in the center). On the right is the $1.24 servo tester.
This board comes up in the mode where output speed is controlled by the pot, pressing a button under the plastic shroud changes between modes. These other modes can be dangerous depending on what mechanism you’re hooking u p to. It might be worth removing the button from the board for safety reasons.
Great advice. I’m going to try a drop of super glue on the button. I’m pretty sure that will work to lock it in place, and it’s way easier than trying to remove the button.
I used Shoe Goo to fasten the servo tester and DC-DC converter to a board.
If the application required precisely 4MHz with little/no drift, then absolutely. Crystal oscillators are both cheap and known for such accuracy, and why many things that don’t require it (such as the AVR328P’s on arduino’s) use them.
As for the 555, probably because it has an easily adjustable duty cycle. In this case the pot is probably stable enough, as the duty cycle is the variable in this circuit and any effects due to heating or the like would scale if it is in the circuit they way I’d expect it to be.
Thus, with a limited number of components one gets an adjustable PWM generator with a precise, stable output frequency.
No documentation is provided for the $1.24 tester. Here’s a picture showing how to connect it.
Note the horizontal orientation of the output connector.
As others have noted, it’s definitely a microcontroller of some sort. My guess would be a low-cost PIC.
My bets are on the PIC16C620A, the package seems to be an SSOP and the pins seem compatible with those that are tied low (or high) in the image you posted. It may be another member of the PIC family, but I’m almost 100% sure that that is a PIC of some kind. You can find them on Digikey if you restrict your search to 20 pin SSOP/SOIC packages, with an external oscillator and what is likely an 8-bit core. Order by cost.